1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device using Plasma-Enhanced Chemical Vapor Deposition (PECVD) method, which includes a step of stabilizing the substrate temperature prior to a step of depositing a dielectric layer. The invention is preferably applied to fabrication of a semiconductor device having a wiring structure or structures formed by using a low dielectric-constant interlayer dielectric layer or layers.
2. Description of the Related Art
In recent years, to solve the problem of RC delay increase in wiring or interconnection lines caused by the constantly progressing miniaturization of semiconductor devices, the use of low dielectric-constant (low k) dielectric materials has been discussed for reducing the line capacitance. For example, the use of a SiOCH layer as the interlayer dielectric layer and the use of a SiCH or SiCHN layer as the dielectric barrier layer or the etch-stop layer have been discussed and researched. These low dielectric-constant dielectric materials are typically deposited by a PECVD method. where the deposition temperature is typically set in the range from 300° C. to 500° C. This is to provide the initial thermal energy required to overcome the reaction barrier. Therefore, a step of stabilizing the substrate temperature at a desired level is required prior to the deposition step of a desired dielectric layer.
FIG. 1 shows a prior-art deposition process sequence for the above-described low dielectric-constant materials using a known PECVD method.
As seen from FIG. 1, in the step S1, a semiconductor substrate or wafer is carried in the reaction chamber of a known PECVD apparatus. In the step S2, a gas is fed into the chamber to stabilize the substrate temperature. i.e., the temperature of the substrate thus carried-in. The gas is used to transmit the heat generated by the heater of the apparatus to the whole substrate, making the temperature substantially steady over the entire substrate.
In the step S3, the chamber is evacuated to remove the gas for stabilizing the substrate temperature from the chamber. In the step S4, a gaseous material or materials (i.e., a deposition gas or gases) for a desired low dielectric-constant dielectric layer is/are fed into the chamber. In the step S5, the desired low dielectric-constant dielectric layer is deposited by a PECVD method on or over the surface of the substrate or wafer using plasma generated in the chamber. In the step S6, the chamber is evacuated to remove the remaining gaseous material(s) (i.e., the remaining deposition gas(es)) and reaction products existing in the chamber. In the step S7, the substrate on which the desired low dielectric-constant dielectric layer has been deposited is carried out from the chamber.
In the prior-art deposition method for the above-described low dielectric-constant materials shown in FIG. 1. nitrogen gas (N2) is usually used as the gas for stabilizing the substrate temperature in the step S2. This is because N2 is low in cost and easy to handle. In this case, however, a problem of the adhesion strength degradation of the deposited low dielectric-constant dielectric layer with respect to an underlying dielectric layer and an underlying copper (Cu) wiring line is likely to occur. According to the inventors' research, it was found that this problem is caused by the following reason.
As shown in Table 1 below, N2 is relatively lower in thermal conductivity among these gases and therefore, the rise of the substrate temperature in the step S2 is relatively slow. Thus, the, subsequent deposition step S5 of the dielectric layer using a PECVD method starts before the substrate temperature rises to a sufficiently high degree. As a result, the quality of the deposited dielectric layer will be low or bad in the initial stage of the deposition step S5, thereby causing the adhesion strength degradation of the deposited dielectric layer to an underlying dielectric layer and an underlying Cu line.
TABLE 1GASTHERMAL CONDUCTIVITY (W/mK)H20.1869He0.1567N20.0260Ar0.0179Xe0.0055
In addition it was reported by Proceeding of IRPS 2000, pp. 339–343 that the Time-Dependent Dielectric Breakdown (TDDB) lifetime between Cu wiring lines (i.e., the inter-wire TDDB lifetime for Cu lines) deteriorates when plasma process using N2 gas is applied to Cu wiring lines prior to the deposition of a silicon nitride (SiN) layer thereon. Thus, there is an anxiety that N2 gas used in the step S2 of stabilizing the substrate temperature is left In the subsequent deposition step S5, thereby inducing the inter-wire TDDB lifetime deterioration. If so, the reliability of the deposited dielectric layer (and therefore, the semiconductor device) will decline.